A transformer can be used to change and transmit electric power from one voltage level to another voltage level. It can also maintain isolation between two voltage level circuitry. Typically, the transformer is one of the heaviest, bulkiest and most expensive parts in a transmission and distribution system. The large size of the transformer is due, in part, to the low frequency of operation. Power density increases as the operating frequency of the transformer increases, resulting in a smaller transformer size and weight. To change operating frequency from a Hz level to a kHz level, power electronics can be used. Power electronics in combination with reduced sized, high-frequency transformers is known as power electronic transformers.